# std::exp2, std::exp2f, std::exp2l

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
| (1) |
float exp2 ( float num ); double exp2 ( double num ); long double exp2 ( long double num ); |  | (until C++23)
/*floating-point-type*/ exp2 ( /*floating-point-type*/ num ); |  | (since C++23) (constexpr since C++26)
float exp2f( float num ); | (2) | (since C++11) (constexpr since C++26)
long double exp2l( long double num ); | (3) | (since C++11) (constexpr since C++26)
SIMD overload (since C++26) |  |
Defined in header `<simd>` |  |
template< /*math-floating-point*/ V > constexpr /*deduced-simd-t*/<V> exp2 ( const V& v_num ); | (S) | (since C++26)
Additional overloads (since C++11) |  |
Defined in header `<cmath>` |  |
template< class Integer > double exp2 ( Integer num ); | (A) | (constexpr since C++26)

1-3) Computes 2 raised to the given power num. The library provides overloads of `std::exp2` for all cv-unqualified floating-point types as the type of the parameter.(since C++23)

S) The SIMD overload performs an element-wise `std::exp2` on v_num. (See `math-floating-point` and `deduced-simd-t` for their definitions.) | (since C++26)

A) Additional overloads are provided for all integer types, which are treated as double. | (since C++11)

### Parameters

num | - | floating-point or integer value

### Return value

If no errors occur, the base-2 exponential of num (2num
) is returned.

If a range error due to overflow occurs, +HUGE_VAL, `+HUGE_VALF`, or `+HUGE_VALL` is returned.

If a range error occurs due to underflow, the correct result (after rounding) is returned.

### Error handling

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

- If the argument is ±0, 1 is returned.
- If the argument is -∞, +0 is returned.
- If the argument is +∞, +∞ is returned.
- If the argument is NaN, NaN is returned.

### Notes

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::exp2(num) has the same effect as std::exp2(static_cast<double>(num)).

For integral exponents, it may be preferable to use std::ldexp.

### Example

Run this code

    #include <cerrno>
    #include <cfenv>
    #include <cmath>
    #include <cstring>
    #include <iostream>

    // #pragma STDC FENV_ACCESS ON

    int main()
    {
        std::cout << "exp2(4) = " << std::exp2(4) << '\n'
                  << "exp2(0.5) = " << std::exp2(0.5) << '\n'
                  << "exp2(-4) = " << std::exp2(-4) << '\n';

        // special values
        std::cout << "exp2(-0) = " << std::exp2(-0.0) << '\n'
                  << "exp2(-Inf) = " << std::exp2(-INFINITY) << '\n';

        // error handling
        errno = 0;
        std::feclearexcept(FE_ALL_EXCEPT);
        const double inf = std::exp2(1024);
        const bool is_range_error = errno == ERANGE;

        std::cout << "exp2(1024) = " << inf << '\n';
        if (is_range_error)
            std::cout << "    errno == ERANGE: " << std::strerror(ERANGE) << '\n';
        if (std::fetestexcept(FE_OVERFLOW))
            std::cout << "    FE_OVERFLOW raised\n";
    }

Possible output:

    exp2(4) = 16
    exp2(0.5) = 1.41421
    exp2(-4) = 0.0625
    exp2(-0) = 1
    exp2(-Inf) = 0
    exp2(1024) = inf
        errno == ERANGE: Numerical result out of range
        FE_OVERFLOW raised

### See also

expexpfexpl (C++11)(C++11) | returns e raised to the given power (\({\small e^x}\)ex) (function)
expm1expm1fexpm1l (C++11)(C++11)(C++11) | returns e raised to the given power, minus 1 (\({\small e^x-1}\)ex-1) (function)
ldexpldexpfldexpl (C++11)(C++11) | multiplies a number by 2 raised to an integral power (function)
log2log2flog2l (C++11)(C++11)(C++11) | base 2 logarithm of the given number (\({\small\log_{2}{x}}\)log2(x)) (function)
C documentation for exp2

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